The present invention relates to sunscreen compositions comprising a dibenzoylmethane derivative, a diester or polyester of a naphthalene dicarboxylic acid and a benzophenone derivative. The sunscreen compositions according to the invention have enhanced photostability.
The prolonged exposure to UV radiation, such as from the sun, can lead to the formation of light dermatoses and erythemas, as well as increase the risk of skin cancers, such as melanoma, and accelerate skin aging, such as loss of skin elasticity and wrinkling. Radiation with wavelengths in the UV-A range (from about 320 to 400 nm) and the UV-B range (from about 280 to about 320 nm) can cause such skin damage, and, thus, sunscreen compositions should preferably comprise both UV-A and UV-B absorbers/reflectors (UV sunscreens). Dibenzoylmethane derivatives, the one of the most commonly used UV-A absorbers, however, suffer from photochemical instability, requiring repeated application to the skin to maintain the desired UV-A protection. See, e.g., Kammeyer, et al., Int. J. Cosm. Sci. 9:125-36 (1987).
Others have recognized this stability problem associated with such UV-A absorbers, and have attempted to find means of stabilizing such compounds. See, e.g., U.S. Pat. No. 5,783,173 (using alkylbenzoates), U.S. Pat. No. 5,993,789 (using diester and/or polyesters of naphthalene dicarboxylic acids), U.S. Pat. No. 5,346,691, PCT Application No. WO98/00099, and European Patent No. 845,260 (using trianilino triazine derivatives with or without derivatives of diphenylcyanoacrylic acid), and U.S. Pat. Nos. 5,576,354 and 6,033,649 (using xcex1-cyano-xcex2,xcex2-diphenylacrylate stabilizer), and European Patent Nos. 514,491, 685,222, and 685,225 (using octocrylene, homomenthyl salicylate, octyl salicylate, and 4-methyl benzylidene camphor to stabilize avobenzone).
U.S. Pat. No. 5,776,439 discloses cosmetic compositions useful for the protection of skin and/or hair from ultraviolet radiations containing photostable mixtures of two sunscreen compounds, sunscreen compound (I) and sunscreen compound (II). Sunscreen agents encompassed by compound I include dibenzoylmethane derivatives such as 4-methoxy-4xe2x80x2tert-butyldibenzoylmethane and 4-isopropyldibenzoylmethane. Sunscreen compound II encompass benzophenone derivatives that were shown to help to stabilize these dibenzoylmethane derivatives. However, there is no teaching or suggestion of the enhanced photostability of the presently claimed compositions as demonstrated by the Examples set forth below.
U.S. Pat. No. 5,993,789 discloses the use of a naphthalene derivative (diethylhexyl 2,6-napthalate xe2x80x9cDEHNxe2x80x9d) in combination with butylmethoxydibenzoylmethane derivatives to photostabilize sunscreen compositions. The patent discusses the use of other commonly utilized sunscreen absorbers in combination with these ingredients (including oxybenzone) to boost the SPF to a level of 20+. This is further disclosed in a publication of Cosmetics and Toiletries (Vol 115: No.6, p. 37-45) with a formulation showing an SPF of 32.8. There is no teaching or suggestion, however, of the enhanced photo-stability of the presently claimed compositions as demonstrated in the Examples set forth below.
The present invention relates to the discovery that a combination of a benzophenone derivative and a diester or polyester of a naphthalene dicarboxylic acid surprisingly increases the photo-stability of dibenzoylmethane derivatives and thereby provide compositions with increased photostabilization.
Accordingly, in one aspect, the invention features a composition comprising: (a) one or more dibenzoylmethane derivative UV-A absorbing agent(s); (b) a diester or polyester of a naphthalene dicarboxylic acid; and (c) a benzophenone derivative, wherein the diester or polyester of naphthalene dicarboxylic acid and benzophenone derivative are present in an amount sufficient to photo-stabilize the dibenzoylmethane derivative and provide a photo-stable sunscreen composition.
Ideally, the optical absorbance of the sunscreen product would stay high no matter how much it was irradiated with sunlight or any artificial UV source. Sunscreen compositions should maintain protection to the skin upon exposure to both the UVB (290-320 nm) and the UVA (320-400 nm) portions of the UV spectrum. The Sun Protection Factor (xe2x80x9cSPFxe2x80x9d) is a measure of the overall biological protection of the sunscreen product against sunburn reactions. PFA is an analogous measure of protection which evaluates the biological protection in the UVA portion of the spectrum. The PFA of a formulation can be determined from clinical trials (Cole, 1991) or can be estimated with in vitro test models. The retention of the biologically weighted PFA value with increasing exposure to UV light is a measure of the photo-stability of the UVA filters in the sunscreen composition (of which the dibenzoylmethane derivative sunscreens are particularly unstable.)
Accordingly, what is meant by to photo-stabilize the dibenzoylmethane derivative is that the diester or polyester of naphthalene dicarboxylic acid and benzophenone derivative are present in amounts sufficient for the composition to maintain a proportion of at least 60% of the original PFA value, preferably, with no measurable degradation with high doses (xe2x89xa750 Joules/cm2) of sunlight or simulated sunlight exposure.
The present invention also features a method of photo-stabilizing a sunscreen composition containing dibenzoylmethane derivative UV-A absorbing agent in a composition comprising adding to said composition an effective amount of a diester or polyester of naphthalene dicarboxylic acid and benzophenone derivative.
The present invention also features a method of protecting skin and hair from UV radiation comprising administering the above compositions.